Perfluoropolyethers: intramolecular disproportionation
TL;DR: In this paper, the thermal degradation of commercial perfluoropolyethers (Fomblin Z and Y, Krytox, and Demnum) and PFPEO (perfluoropoly(ethylene oxide)) in the presence of Lewis acids (metal oxides and halides) was examined.
Abstract: Thermal degradation of commercial perfluoropolyethers (Fomblin Z and Y, Krytox, and Demnum) and PFPEO (perfluoropoly(ethylene oxide)) in the presence of Lewis acids (metal oxides and halides) was examined. It is shown that the degradation is dominated by the intramolecular disproportionation process of the following scheme RCF 2 OCF 2 (CH 2 ) 3 OR → RCOF + CF 3 (CH 2 ) 3 OR. The reaction occurs when the two oxygen atoms flanking a monomer unit of polyether chains interact with a Lewis acid site(s). The differentail charges induced at the carbons immediately outside and inside the unit cause a fluorine transdfer and effect the disproportionation process
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TL;DR: Several approaches have been taken to lubricate this microelectromechanical system (MEMS) device and to reduce the adhesion between its contacting surfaces as mentioned in this paper, including self-assembled monolayers (SAMs), fluids, and solid lubricants.
Abstract: Nearly fifty lubricants have been investigated for use in theDigital Micromirror DeviceTM (DMDTM). Theexploration has ranged from self-assembled monolayers (SAMs),to fluids, to solid lubricants. This paper discusses several ofthe various approaches that have been taken to lubricate thismicroelectromechanical systems (MEMS) device and to reduce the adhesion between its contacting surfaces.
141 citations
TL;DR: In this paper, the surface chemistry of ionic liquid lubricated steel in sliding contact to temperatures from room to 300°C was studied using a pin on disk tribometer with high temperature capability.
Abstract: Ionic liquids have properties that make them attractive as solvents for many chemical synthesis and catalysis reactions. Consequently, research has focused on their application as advanced solvents. Recently, ionic liquids were shown to have promise as a lubricant due to many of the same properties that make them useful as solvents. The focus of this paper is to study the surface chemistry of ionic liquid lubricated steel in sliding contact to temperatures from room to 300 °C. Tribological properties were evaluated using a pin on disk tribometer with high temperature capability (up to 800 °C). Chemistry was studied using Mossbauer spectroscopy and X-ray photoelectron spectroscopy. Samples used for tribological evaluation were 1 inch diameter polished M50 disks. Samples used for studying the surface chemistry were enriched 57Fe grown via thermal evaporation. Some 57Fe samples were oxidized to Fe2O3 and Fe3O4 prior to treatment with ionic liquids. The metallic and oxidized 57Fe samples were then reacted with ionic liquids at elevated temperatures. Three ionic liquids were used in this study; 1-n-ethyl-3-methylimidazolium tetrafluoroborate (BF4), 1,2-di-methyl-3-butylimidazolium bis(trifluoromethylsulfonyl)imide (TFMS), and 1,2-di-methyl-3-butylimidazolium hexafluorophosphate (PF6). This study was focused on understanding the high temperature stability of the liquids in contact with metal and under tribological stress. Therefore, the friction data was collected in the boundary (or mixed boundary/EHL) lubrication region to enhance surface contact. BF4 provided a friction coefficient of 0.04 for both the room and 100 °C tests and varied between 0.07 and 0.2 for the 300 °C test. The results from TFMS lubrication showed a friction coefficient of 0.025 at room temperature and 0.1 at 100 °C. The 300 °C test friction coefficient ranged between 0.1 and 0.3. Chemical analysis of the surface revealed corrosion of the surface due to reaction between the ionic liquids and steel/iron substrates.
95 citations
IBM1
TL;DR: In this paper, it was shown that perfluoropolyethers (PFPE) with carboxylic acid end groups, PFPE-COOH, and their sodium salts, P FPE-COONa, afford an anhydrous fluid medium in which the direct pair-wise interaction of these end groups may be examined.
Abstract: It was found that perfluoropolyethers (PFPE) with carboxylic acid end groups, PFPE-COOH, and their sodium salts, PFPE-COONa, afford an anhydrous fluid medium in which the direct pair-wise interaction of these end groups may be examined. An IR study (of the carbonyl band) of these materials revealed not only the dimerization of acid units, but also the formation of salt dimers, (salt)2, and mixed dimers, (acid)(salt). The carbonyl spectra of PFPE-acid/salt mixtures exhibit temperature-dependent broadening, shift, and, in some cases, coalescence of the bands which are attributed to the pseudocoalescence phenomenon stemming from the presence of relatively low energy cation exchange passages among the three possible dimers. Examination of the corresponding CH3COOH/CH3COONa system by ab initio calculations (6-31G) yielded the heat of dimerization of ∼20, ∼50, and ∼35 kcal/mol for the acid−acid, the salt−salt, and the acid−salt dimers, respectively. The calculated dimer structures are shown and discussed. The c...
80 citations
TL;DR: In this paper, the use of PFPEs to coat nano-aluminum (n-Al) and under optimized stoichiometric formulations, harnessed optimized energy output was employed.
Abstract: Fluoropolymers have long served as potent oxidizers for metal-based pyrolant designs for the preparation of energetic materials. Commercial perfluoropolyethers (PFPEs), specifically known as Fomblins®, are well-known to undergo accelerated thermal degradation in the presence of native metals and Lewis acids producing energetically favorable metal fluoride species. This study employs the use of PFPEs to coat nano-aluminum (n-Al) and under optimized stoichiometric formulations, harness optimized energy output. The PFPEs serve as ideal oxidizers of n-Al because they are non-volatile, viscous liquids that coat the particles thereby maximizing surface interactions. The n-Al/PFPE blended combination is required to interface with an epoxy-based matrix in order to engineer a moldable/machinable, structurally viable epoxy composite without compromising bulk thermal/mechanical properties. Computational modeling/simulation supported by thermal experimental studies showed that the n-Al/PFPE blended epoxy composites produced an energetic material that undergoes latent thermal metal-mediated oxidation. Details of the work include the operationally simple, scalable synthetic preparation, thermal properties from DSC/TGA, and SEM/TEM of these energetic metallized nanocomposite systems. Post-burn analysis using powder XRD of this pyrolant system confirms the presence of the predominating exothermic metal-mediated oxidized AlF3 species in addition to the production of Al2O3 and Al4C3 during the deflagration reaction. Details of this first epoxy-based energetic nanocomposite entrained with a thermally reactive formulation of PFPE coated n-Al particles are presented herein.
79 citations
TL;DR: The perfluoropolyether (PFPE) class of liquid lubricants has been used for space applications for over two decades as discussed by the authors, however, as other spacecraft components have become more reliable and lifetimes have been extended, PFPE lubricant deficiencies have been exposed.
Abstract: The perfluoropolyether (PFPE) class of liquid lubricants has been used for space applications for over two decades. At first, these fluids performed satisfactorily as early spacecraft placed few demands on their performance. However, as other spacecraft components have become more reliable and lifetimes have been extended, PFPE lubricant deficiencies have been exposed. Therefore, the objective of this paper is to review the PFPE properties that are important for successful long term operation in space.
71 citations